1. Field of the Invention
The present invention pertains to fuel cell power plants and, more particularly, to a coolant system for an integrated fuel cell power plant.
2. Description of the Related Art
Fuel cell technology is an alternative energy source for more conventional energy sources employing the combustion of fossil fuels. A fuel cell typically produces electricity, water, and heat from a fuel and oxygen. More particularly, fuel cells provide electricity from chemical oxidation-reduction reactions and possess significant advantages over other forms of power generation in terms of cleanliness and efficiency. Typically, fuel cells employ hydrogen as the fuel and oxygen as the oxidizing agent. The power generation is proportional to the consumption rate of the reactants.
A significant disadvantage which inhibits the wider use of fuel cells is the lack of a widespread hydrogen infrastructure. Hydrogen has a relatively low volumetric energy density and is more difficult to store and transport than the hydrocarbon fuels currently used in most power generation systems. One way to overcome this difficulty is the use of “fuel processors” or “reformers” to convert the hydrocarbons to a hydrogen rich gas stream which can be used as a feed for fuel cells. Hydrocarbon-based fuels, such as natural gas, LPG, gasoline, and diesel, require conversion for use as fuel for most fuel cells. Current art uses multi-step processes combining an initial conversion process with several clean-up processes. The initial process is most often steam reforming (“SR”), autothermal reforming (“ATR”), catalytic partial oxidation (“CPOX”), or non-catalytic partial oxidation (“POX”). The clean-up processes are usually comprised of a combination of desulphurization, high temperature water-gas shift, low temperature water-gas shift, selective CO oxidation, or selective CO methanation. Alternative processes include hydrogen selective membrane reactors and filters.
Thus, many types of fuels can be used, some of them hybrids with fossil fuels, but the ideal fuel is hydrogen. If the fuel is, for instance, hydrogen, then the combustion is very clean and, as a practical matter, only the water is left after the dissipation and/or consumption of the heat and the consumption of the electricity. Most readily available fuels (e.g., natural gas, propane and gasoline) and even the less common ones (e.g., methanol and ethanol) include hydrogen in their molecular structure. Some fuel cell implementations therefore employ a “fuel processor” that processes a particular fuel to produce a relatively pure hydrogen stream used to fuel the fuel cell.
A processor for a typical Polymer Electrolyte Fuel Cell (“PEFC”), also known as Proton Exchange Membrane Fuel Cell (“PEMFC”), generally comprises of reactor sections for hydrocarbon reforming, water gas shift and oxidation reactions. The reactions are carried at elevated temperatures and are a combination of heat generating, heat consuming or constant temperature variety. Therefore, heat management is critical for proper operation of the processor. Hot reaction products can be used to preheat the reactants, while cooling the products, thus managing the heat within the processor. One difficulty with conventional cooling subsystems is the dependence between the reactor cooling and the temperatures of the reactor feeds and products. Another problem is that the fuel cell power plant, i.e., the fuel cell and its fuel processor, are frequently housed in a cabinet, which causes additional heat management problems. Conventional approaches to these problems applies a separate cabinet cooler. However, the separate cabinet coolers adversely impact the power and cost efficiencies of the power plant as a whole.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.